Thermal sensing of liquid through the wall of standard tubing is generally impeded by the amount of surface contact between the tube and the sensing die. If thermal properties of liquid could be accurately sensed through the tubing, then the flow of liquid as it is passing through standard tubing could also be sensed. Physical contact between tubes and sensors is not typically much more than the point or line of contact where the outer radius of the tubing diameter contacts the flat surface of a die adapted with thermal a sensor.
Thermal flow sensors rely on the change in tubing wall temperature to sense the amount of flow through the tubing. To enhance sensitivity of a thermal flow sensor, it would be beneficial if more area of the standard tubing were in thermal contact with the sensing die.